This thesis is a study of the development of investigatory select committees of the House of Commons during the twentieth century, with a particular emphasis on the period between 1960 and 1990. Synthesising existing analysis as well as presenting new evidence, it describes the early origins of such committees as an integral part of the work of the House, and then considers the Houseâs apparent loss of interest in select committees between 1920 and 1960. The thesis next discusses the reasons behind the introduction of new select committees in the mid-1960s, and traces further changes to committees during the 1970s. These developments are set in the political context of the period, and in particular the growth of backbench dissent in both major parties during the 1970s. The thesis then analyses the process by which departmentally-related select committees came to be established in 1979. Finally it assesses the quantitative and qualitative evidence about the activity and impact of the new departmental select committees in their first decade up to 1990, relating them closely to the political environment created by the government of Margaret Thatcher.